1. Field of the Invention
This invention generally relates to systems steam reforming of hydrocarbon fuels to generate hydrogen rich reformate for use in fuel cells.
2. Background Information
As a part of the overall strategy to try and find cleaner and more efficient methods of providing power, new fuels and systems have and continue to be developed. Among these technologies and devices are so called fuel cells, particularly polymer electrolyte fuel cells (PEFCs). These devices generally require hydrogen fuel to operate and when provided with these materials provide a clean and reliable energy source. However, the difficulty in safely and efficiently storing and distributing hydrogen typically limits the practical use of such devices.
To attempt to remedy this problem a fuel processor using the steam reforming reaction can be used to liberate hydrogen from a hydrocarbon fuel to provide hydrogen at the point of use for a fuel cell. Among the potential hydrocarbon sources that may be reformed to generate hydrogen are lower volativity fuels with high boiling ranges such as home heating oil, diesel fuel, JP-8, and other similar hydrocarbon fuels.
The reformation process typically involves the conversion of a hydrocarbon to a mixture of carbon dioxide, carbon monoxide and hydrogen, along with residual amounts of methane. Before introducing the fuel into the reforming reactor, the fuel must be brought into the vapor phase and mixed with steam. However, the boiling range of these hydrocarbons is close to the temperatures at which breakdown of the hydrocarbons may begin to occur which increases the potential for formation of carbon deposits within the reforming system. The formation of carbon deposits may adversely affect the reformer performance by reducing catalyst activity or by obstructing flow passages.
The tendency for the formation of deposits increases as the temperature increases. Because the typical reformation process requires elevated temperatures to vaporize, preheat and then react these materials, the formation of carbon deposits is a frequent problem. Furthermore, once these processes of contaminant creation and carbon deposition begin, it is very difficult for these processes to be reversed, and the susceptibility of the system to further influence by these materials is increased.